How to connect shape key animation as driver to rotate a bone in pose mode
i managed to write one. if anyone else looking for same thing, below is simple function to test and could be starting point. 
select facecap head mesh and rigify jaw master (in pose mode)

def bindFacecapToRigify():
    obj = bpy.context.selected_objects[0]
    sk = obj.data.shape_keys
    # driver details (skname:'pbone','prop','axis','dir'),
    skname = 'jawOpen'
    pbone = bpy.context.active_pose_bone
    d = pbone.driver_add("rotation_euler",0)
    d.driver.type = "AVERAGE"
    var = d.driver.variables.new()
    var.targets[0].id_type="KEY"
    var.targets[0].id= sk
    data_path = "key_blocks[\""+sk.key_blocks[2].name+"\"].value"
    data_path = "key_blocks[\""+"jawOpen"+"\"].value"
    var.targets[0].data_path = data_path
    d.driver.expression = "var"